Static vs Dynamic Routing

[john-lucero]

I have a small network consisting of about 12 segments 3 WAN connections and access to the Internet over T1. I have several routers with in my LAN that support various functions and system. All act as gateways to different networking systems.

I perfer to use Static routing over dynamic routing. I feel that I like to know specificaly how traffic is being routed, and have greater control.

My question is am I kidding myself by perfering to use the static routes? Am I running into any pit falls that may cause me serious problems?

Your input would be appreciated.

[cjnwodo]

John,

In a very very small network, static routes are ok, for the sake of simplicity; however as the network begins to grow, the administrative overhead of adding/removing more static routes becomes a nightmare !!

Hence dynamic routes come into their own- RIPv2, OSPF, EIGRP, BGP etc

There are some pitfalls with static routes, for example imagine [rather simplistic situation]:

RTA--RTB--RTC--RTD

If on RTA you had to add a static route to the LAN hanging off RTD, the next hop will be RTB. If the WAN between RTC and RTD was down RTA has no way of knowing, and will still send the 'doomed' packets to RTB where the same applies. RTB will forward the packets to RTC who will bin them because RTD is now unavailable. Imagine all the bandwidth that will have been chewed up as these packets traverse the WAN assuming there were 20Meg files FTPed across T1 WAN circuits. With a routing protocol, RTA will bin them straight away.

[rjackson]

static routes are good for pointing to remote stubs. You put static routes in the WAN router pointing to those networks and static defaults in the remote routers pointing back to the core via the WAN router.

If you want to avoid having to put statics in the other LAN router you can run a simple routing protocol between the lan and wan routers at the core. Your choice should depend on how much you think things will be changing. It is much easier to make changes using a dynamic routing protocol in the core.

[cymurai]

I agree with the other two posts, static routes are fine if you only have directly connected routers. As soon as traffic needs to go THROUGH a router to a third distant router, you are destined for trouble if the route no longer exists. A better way, if it suits your needs, would be to implement ODR in a hub/spoke config. It is dynamic in nature, but acts much the same as static routes. Otherwise, some other routing protocol should be used, unless your positive your links will always be up.

More info:

http://www.cisco.com/en/US/products/sw/iosswrel/ps1828/products_configuration_guide_chapter09186a00800ca567.html

Hope this helps!